JPS5988719A - Polyester film for base material of liquid crystal panel - Google Patents

Abstract

PURPOSE:To provide a polyester film made of terephthalate- or 2,6-naphtalate- polyester which has a specified birefringence index and haze and is improved in the coloring due to interference fringes. CONSTITUTION:The polyester film of this invention is made of terephthalate- or 2,6-naphtalate-polyester and has a birefringence index of 30X10<-3>-110X10<-3>, a thickness of 100mum, and a haze of <=5%. It is desirable to use a polyester whose transparency is not lowered and dimensions are not changed when heated, since the film is put in a heated condition at the time of manufacturing liquid crystal panels. It is desirable from the point of practical use that the coefficient of contraction is <=5% when held in a 150 deg.C atmosphere for 30min and the haze is <=5% at a thickness of 100mum. These conditions are achieved when a film of >=30X10<-3> in the degree of surface orientation is heat treated so that its mean refractive index becomes >=1.595 in the manufacturing process of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyester film for liquid crystal panel substrates.

Glass plates have traditionally been widely used as liquid crystal panel substrates. Although glass plates are excellent base materials in terms of performance, they are brittle against impacts.

Moreover, it is difficult to make it thin due to the mechanical strength. Therefore, the use of plastic films as base materials for liquid crystal panels in place of glass plates is being considered. Liquid crystal panels based on glass film are flexible,
It is expected to exhibit properties that cannot be achieved with glass, such as lightness, processability, impact resistance, and thinness.

Various types of glass films have been proposed for use as substrates for liquid crystal panels, but from the viewpoint of heat resistance, moisture resistance, chemical resistance, mechanical strength, etc.
Naphthalate polyesters are promising.

Plastic film for LCD panel substrates.

It must be something that does not narrow the appropriate viewing angle as a panel and does not reduce readability as a liquid crystal display device.

To achieve this, when the film is sandwiched between two polarizing plates,
It is necessary that no interference fringes occur when viewed from any direction. Conventionally, in order to satisfy this condition, it has been necessary that the retardation value (R value) of the film be less than rOmμ (see Publication No. 220, 1987-//f).

However, according to the inventor's study, in a liquid crystal panel based on a terephthalate or naphthalate polyester film, the R value of the film is! It has been found that even though there are no interference fringes when viewed from directly above, there is coloring due to interference fringes when viewed from a different direction in the Yang Kai below θmμ. This is the result of the inventor's study on this point.

In particular, if a highly oriented film, that is, a film with a large R value, is assembled into a panel so that the polarization axis of the polarizing plate and the ball axis of the film coincide, interference fringes will be generated when viewed from any direction. The present invention was completed based on the discovery that no rock color occurs due to

That is, the gist of the present invention is that it is made of terephthalate or naphthalate polyester, has a birefringence of 3θ×/θ−3 to //θ×/θ4, and has an iooμ
Haze at a thickness of ! The present invention relates to polyester films for LCD panel substrates, which are characterized by having a polyester film of less than 10%.

To explain the present invention in detail, the terephthalate or 6-naphthalate polyester used in the present invention is a polyester containing terephthalate, 6-naphthalene dicarboxylic acid as the main acid component and ethylene glycol as the main glycol component. . Some of the terephthalic acid and di-naphthalene dicarboxylic acids are isophthalic acid, heptalic acid, adipic acid, and sebacic acid.

It may be substituted with a polyfunctional carboxylic acid such as succinic acid, p-hydroxybenzoic acid, and ω-hydroxycaproic acid. Similarly, a portion of ethylene glycol may also be substituted with a polyhydric alcohol such as trimethylene glycol, hexamethylene glycol, cyclohexane dimetatool (/, Q), polyethylene glycol, or the like. Usually +L/7 talic acid or 6-naphthalene dicarboxylic acid component and ethylene glycol component, respectively? θ mol% or more, preferably r/′i90
A polyester having a molar coefficient or higher is used. The most commonly used polyester is a polyester made from a terephthalic acid or 6-naphthalene dicarboxylic acid component and ethylene glycol.

In addition to the components that are necessarily mixed, the film may contain various additives commonly used in the production of polyester films, such as stabilizers, ultraviolet absorbers, and lubricants. However, since the film according to the present invention is required to have transparency and surface smoothness, the polyester should be substantially free of particles.

4- or those containing only extremely fine particles are preferred. Such polyesters are produced by: 1. For example, in the polycondensation process of transesterification products, a phosphorus compound such as ethyleneamide phosphate is added to precipitate fine particles containing calcium or calcium and lithium and phosphorus, which are used as transesterification catalysts. It can be manufactured by Furthermore, a polyester that provides a film with excellent transparency and surface smoothness can also be produced by adding a small amount of ultrafine particles such as silica or kaolin to a polyester that does not contain any particles.

The polyester film according to the present invention can be produced using the above-mentioned polyester using the usual film manufacturing method, that is, extruding molten polyester into a sheet form from an extruder, bringing it into contact with a cooling roll to rapidly solidify it, then stretching, and then heat setting. can be manufactured by the method of When bringing the molten polyester sheet into contact with the cooling roll.

In order to produce a film with good thickness accuracy at high speed, it is preferable to use the so-called electrostatic cooling method ki4 (see Japanese Patent Publication No. 37-G/Gu). Since the electrostatic cooling method is difficult to apply to polyester, which has a high specific resistance when melted, the specific resistance of melt P1 Tanukishi is O×/θ for polyester.
' It is preferable to use one with a diameter of 12 cm or less.

Stretching and heat setting are performed until the resulting film has a refractive index of 3.
0×10−3 to /lθ×/θ−3, and /θθμ
The haze in the middle of nowhere! Do this so that you can get a high yield. This condition is 1. For example, the degree of plane orientation in the longitudinal direction of an unstretched film is 3.
This is achieved by stretching the film until a film of θ x 70"" or more and with little thickness unevenness is obtained, gripping the film with tenter clips, and heat-setting it without transverse stretching.

If the degree of plane orientation is as small as 3θ x 70'', the film tends to undergo non-uniform shrinkage during heat setting, resulting in large thickness unevenness or formation of monospherulites, resulting in whitening of the film.

Note that if the longitudinal stretching ratio becomes too large, it will be easy to avoid in the stretching direction, so care must be taken. In order to avoid this, it is also possible to adopt a method in which the film is stretched in the vertical direction and then slightly stretched in the horizontal direction.

Another method is to stretch in the longitudinal direction at a low magnification before reaching the yield point on the stress-strain curve, then stretch in the transverse direction with a tenter, and then heat set, so that the refractive index in the transverse direction is the same as the refractive index in the longitudinal direction. It may also be a large film. Also, how thick is the film thus obtained? Especially under high yield conditions! It is preferable that the yield is high. Films with large thickness unevenness.

This is disadvantageous because it is necessary to select and conveniently use parts of the film that are attractive.

The thickness of the film is 70~! θθμ is appropriate, preferably! θ~200μ.

If the film is too thin, the so-called 1-thickness will be weakened, and if it is too thick, it will not meet the demand for thinner LCD panels.

In addition, the film according to the present invention must have a birefringence of jOXlo-" to /10x10-" with a high flux density. Haze! However, large films have poor transparency, making it difficult to read characters, figures, symbols, etc. displayed on a liquid crystal panel. Also, if the birefringence is smaller than 30X10-3,
When used as a liquid crystal panel, interference fringes occur, reducing readability. However, if the birefringence is larger than 1/θ×10', the film will be difficult to avoid, and it will be difficult to slit it into a product during manufacture or into a liquid crystal panel plate, which is undesirable.

It is desirable that the film according to the present invention further has good heat resistance. In other words, in the production of liquid crystal panels, films are often subjected to heating conditions in order to form a conductive film on the film, etc., so that heating does not cause changes in 91 dimensions that reduce transparency. It is desirable that the From a practical point of view, /! 30 in the atmosphere of O'Q,
The shrinkage rate when held for minutes! p under high yield, and 10
The haze at a thickness of θμ! It is desirable to have high yields. According to the inventor's study, this condition is established in the film manufacturing process.

The total average refraction of a film with a plane orientation of 3θX10”-” or more
8- Achieved by heat treatment so that the refractive index becomes Zj 96 or more.

As detailed above, the film for liquid crystal panel substrate according to the present invention has a thickness of /θ0μ! Haze under high yield and 30
It has a birefringence of ×10-”~//θX/0-”, and liquid crystal panels manufactured using it do not generate interference fringes depending on the viewing direction, and have excellent readability. There is.

Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the Examples having a diameter of 9° or less unless it exceeds the gist thereof.

Note: 1. Thickness unevenness and heat shrinkage rate in this specification.

Average refractive index, degree of one-plane orientation, ? The lJ refractive index, film haze, and interference fringes were measured by the following methods.

(b) Thickness unevenness Using a continuous film thickness measuring device (using an electronic micrometer) made by Anki Denki Co., Ltd., measure the thickness of the film along the main axis direction of the film.
711 was measured and calculated using a linear equation.

(b) Cut out test pieces of 300 g x / j nm each along the ball axis direction of the heat shrinkage film and the direction perpendicular to this, and hold one end of each specimen in a hot air circulation furnace maintained at 15θ"C. Hanging.

Heat treatment was performed for 30 minutes. The longitudinal dimensions of the test piece before and after heat treatment were calculated, and the heat shrinkage rate was calculated using a linear equation.

Heat recovery IF5 rate - (length before heat treatment - length after heat treatment) /
Length before heat treatment Obtain the maximum refractive index nM in the plane of the film using a sodium lamp, the refractive index nβ in the direction perpendicular to it, and the refractive index na in the thickness direction, and calculate the average refractive index, refractive index, and degree of plane orientation by the following formula: Calculated according to

Birefringence = nza - nβ) Birefringence was determined using an integrating sphere digital turbidity meter NDH-20D manufactured by Nippon Arashiki Kogyo Co., Ltd. according to film base ASTM-D-/θ03.

7 I/l/ The total thickness of the film d (μ), the measured value of film haze is HIm, and the measured value of haze after applying liquid paraffin to the film surface is assumed to be 4.

For a film with a thickness of 100μ, -XHVi is determined by the following equation.

(E) Interference fringes - First, stack one polarizing plate in a direction in which the polarizing axes are perpendicular to each other, then sandwich a film between the polarizing plates so that the polarizing axis of the polarizing plate and the ball axis 11 of the film coincide in one direction. do. When held up to sunlight and viewed from all angles in this condition, those that did not change color due to interference were evaluated as good, and those that changed color depending on the angle were evaluated as poor.

Example/ 700 parts of dimethyl terephthalate (sword (Okibe).

Hereinafter, unless otherwise specified, parts are indicated by N. ).

30 parts of ethylene glycol and 90 parts of magnesium acetate tetrahydrate were placed in a reactor and heated to raise the temperature, and methanol was distilled off, and the temperature was raised to 230° C. over a period of approximately 3 hours to complete the ester conversion reaction. Next, parts of ethyl acid phosphate θ, 04 and parts of antimony trioxide θ, 04 were added to this reaction product, and polymerized according to a conventional method to produce a polyester having a specific resistance of 3.0×/θ-70/m. Got a tip.

This chip was vacuum dried at /4θ°0 for 70 hours.

Melt at λ = 0 °C, extrude through a T-die, and rapidly cool using the electrostatic cooling method.3! An unstretched film of θμ was obtained. This unstretched film was stretched 3.5 times in the machine direction at 7°C, and then fed into a tenter with the horizontal stretching machine level 12 straight to prevent stretching. Heat set for 70 seconds with
A uniaxially stretched film of θθμ was obtained. The physical properties of the obtained film are shown in Table 1.

Comparative example / Thickness /! The longitudinal stretching ratio of the unstretched film of θμ is /,! A uniaxially stretched film with a thickness of 700 μm was obtained in the same manner as in Example except that the film was doubled. The physical properties of this film are shown in Table 1.

Example λ In Example/, an unstretched film i having a thickness gtθμ
(+' 7 '(l) after being stretched by /,! times in the machine direction and then 3.3 times in the cross direction at 10θ°C.

The film was heat-set at 220° C. for 10 seconds to obtain a biaxially stretched film having a thickness of /θθμ. The physical properties of this film are shown in Table 1.

Example 3 Except that heat fixation was performed at 730°C for 70 seconds.

A biaxially stretched film was obtained in the same manner as in Example.

The physical properties of this film are shown in Table 1.

Comparative Example 2 In Example/, the unstretched film with /0θμ? 7
After stretching 3.6 times in the machine direction at 0 °C, then stretching 3.2 times in the direction of the oak at 700 °C, heat-setting at 220 °0 for 70 seconds to obtain a biaxially stretched film with a thickness of /θ o μ. ? 0. The physical properties of this film are shown in the table below.

Claims (1)

[Scope of Claims] (1) Made of terephthalate or 2,6-naphthalate polyester, with a birefringence of 3θ×70−”~/
The haze is lθ×/θ−3 and the thickness is /θθμ! A polyester film for a liquid crystal panel substrate, characterized in that the polyester film has a +21 The polyester film according to claim 1, which is characterized in that the average refractive index is 7.396 or more 0 (3)/! When held at tO℃ for 3θ minutes, the haze at a thickness of /θθμ is less than that, and the shrinkage rate is! 3. The polyester film according to claim 1 or 2, characterized in that the polyester film has a polyester film of less than or equal to (4) Uniaxially or biaxially stretched polyester film with a degree of plane orientation of 30x/θ-3 or more f/15'0°C to 2&j
The polyester film according to any one of claims 1 to 3, wherein the polyester film is heat-set with O.